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Institut für Wasserbau - IWS

Selected Topics and International Network Lectures (SS 2007)


noch laufendeSS-2008WS-2007/08SS-2007WS-2006/07SS-2006WS-2005/06SS-2005WS-2004/05(vor WS-2004/05)

16:00 Uhr
Anongnart Assteerawatt, M.Sc.
Lehrstuhl für Hydromechanik und Hydrosystemmodellierung

"Modelling Fractured Systems: Geo-Statistical and Stochastic Fracture Generation"

By applying a discrete model approach to study flow and solute transport processes in a fractured system, the effect of indiviual fractures can be explicitely investigated. The critical step for a discrete fracture model is the generation of a ``representative'' fracture network that can accurately capture the behavior of a fractured aquifer system. The stochastic fracture generation rely on the statistical distribution of fracture geometries, such as orientation, density, aperture or length, however, not the spatial connectivity between fractures. In this talk, the geo-statistical fracture generator which accounting for both fracture geometries and the spatial connectivity will be presented and its results will be compared with the one from the stochastic fracture generation.

Based on the geostatistic approach, different realizations of the same descriptions can be generated, hence, an overall behavior of the fracture-matrix system have to be investigated from many realizations which means high computational demand. Due to this, the streamline method is an attractive alternative to overcome the computational cost. The streamline approach for solute transport in a fracture-matrix system will presented and the results will be discussed and compared with the results obtained from solving a mass conservative transport equation.

16:00 Uhr
Stefan Dwenger

"Transport Interactions between Gas and Water in thin Hydrophobic Porous" (first results)

16:00 Uhr
Jan Nordbotten
Bergen University, Norway

On the relationship between the multiscale finite volume method and domain decomposition preconditioners

In this talk we review the classical non-overlapping domain decomposition (NODD) preconditioners, together with the newly developed multi-scale control volume (MSCV) method. By comparing the formulations, we observe that the MSCV method is a limited special case of a NODD preconditioner. We go on to suggest how the more general framework of NODD can be applied in the multi-scale context to obtain improved multi-scale estimates.
These results are placed in the setting of a more general comment on the development of multi-scale method.

16:00 Uhr
Phillip Binning
Technical University of Denmark

Assessing the risk of contaminated sites: Monitoring mass discharge from contaminant point sources and catchment scale assessment of risk

Ranking of the risks associated with contaminated sites is important when prioritizing remediation effort for a groundwater catchment. Here methods for monitoring contaminant mass discharge from individual sites are tested in a field study at a contaminated site. The results are then put into the context of an assessment of the relative risk of all contaminated sites located within the catchment.

Risk assessments are typically built on measurements of groundwater contaminant concentrations. It can be argued that the mass discharge, which is a measure of the total contaminant load passing an area over time, is a better measure for determining risk. Results from an extensive field campaign aimed at measuring mass discharge of TCE at a contaminated site are reported. It is shown that in the unsaturated zone, vapour phase diffusion can be an appreciable mechanism for spread of contamination. Down stream of the site, various methods for determination of mass discharge including integrated pumping and conventional monitoring are compared.

Results from the field campaign are then included in a catchment scale assessment of risk. Current risk assessment tools are of limited use when determining downstream impacts because they focus on groundwater impacts at, or near, a given contaminant source. Here a new integrated risk assessment tool is developed with the aim of determining impacts on downstream water supply wells and prioritizing the clean up of contaminated sites within a given groundwater catchment. The catchment scale risk assessment tool was used to find the most likely source of the contamination and to rank the risk of known contaminated sites in the catchment. It was shown that a deep free phase plume of TCE is likely to be present at one site. Field work is presented to confirm this hypothesis. The risk assessment has also provided insight into the effectiveness of the pump and treat containment scheme being employed in the

16:00 Uhr
Jing Li
Institut für Wasserbau
Lehrstuhl für Hydrologie und Geohydrologie

Simulation of random fields using non-Gausssian dependence

As flow and transport simulations are often used for environmental risk assessment (for example the contaminant plume underground) and the flow behavior is considerably influenced by the spatial structure of heterogeneous hydraulic conductivity fields, it is of vital importance to clarify the role of spatial dependence structures for the estimation of flow and transport. In the traditional spatial simulations, a multivariate lognormal distribution is often assumed for the conductivity fields, which contradicts the usually non-Gaussian distribution of conductivities in reality. Moreover the sole descriptor for spatial dependence which is used by the multi-Gaussian assumption fails to characterize the often occurred deviation from the central tendency. Therefore there is a need for new non-Gausssian simulation methods and hence for new types of random functions. Recently, copulas have been evoking considerable interest in financial mathematics because they provide an innovatory way of modeling the dependence structure between variables. Our research is carried out to develop new families of random functions with distinct non-Gaussian properties for spatial simulations of hydraulic conductivities. In the presentation, at first, a brief introduction for the concept of copulas and dependence will be given. Second, the methodology of using copulas to investigate spatial variabilities will be presented. Third, several random fields of hydraulic conductivity with arbitrary marginal distributions and a given copula will be demonstrated and compared. Finally, the approach of Euler characteristics to study the connectivity of the fields will be discussed.

16:00 Uhr
Suze Anne Korteland
Utrecht University

Averaging the equilibrium capillary pressure-saturation relationship

In my master research, I investigate the effect of different averaging methods on the sample-scale equilibrium Pc-Sw relationship. Further, I investigate what factors influence the residual wetting phase saturation that can be reached in a sample column. I do this by performing numerical simulations. The results show that the capillary pressure-saturation relationship at the sample scale is not an intrinsic property of the porous medium, but dependent on factors such as measurement techniques, boundary conditions, or averaging methods.

16:00 Uhr
Prof. Dr. M.A. Efendiev
TU München
Institute of Biomathematics and Biometry, GSF
National Research Center for Environment and Health

Hydrodynamics and biofilms

We deal with a new class of equations arising in the modelling of biofilms. Based on the experimental observations we will derive these equations. Both hydrostatic and hydrodynamic effects will be taken into account. Some open problems will be discussed.

17:00 Uhr
Yufei Cao
Institut für Angewandte Analysis und Numerische Simulation

Studies of mortar finite volume element methods and fractional flow formulation for two-phase flow in porous media

With the rapid development of computational mathematics, discretization methods using domain decomposition concept are becoming powerful tools to handle real-life problems with complicated domains or complex processes, and have the capabilities of high performance computation to large-scale problems. Mortar finite element method is one of the domain decomposition methods which allows the coupling of different physical models, numerical schemes and non-matching grids along interior interfaces of the computational domain. Therefore, there has been growing interest in the mortar finite element method due to its flexibility and great potential for large-scale parallel computation. On the other hand, the finite volume element methods are popular in computational fluid mechanics since they can keep the properties of original problems, i.e., satisfy discrete local mass conservation which is the most desirable feature of the numerical methods for many applications. Combining the above two methods, mortar finite volume element(MFVE) method is formed. Due to the advantages combination of flexibility and local conservation, it's attractive to solve porous media flow problems using MFVE method. Therefore, MFVE methods for simple models including stationary elliptic problems and time-dependent parabolic problems are first studied in the presentation. Furthermore, in order to implement MFVE methods into multi-phase flow problems in porous media, the fractional flow formulation for two-phase flow is then carefully studied in comparison with the fully coupled formulation including numerical solutions, adaptive possibilities and other application: time-of-flight simulation.